Vibronic structures of the ground and first excited electronic states of aromatic hydrocarbons cooled in supersonic jet

The fluorescence excitation and dispersed fluorescence spectra of pyrene and acenaphthene molecules cooled in a supersonic jet have been obtained. Based on the K. Ohno MO/8 model, a new method for calculating frequencies of the inplane vibrations in the excited electronic states of polycyclic aromatic hydrocarbons is developed. It is shown, that for investigated molecules the prediction accuracy of the vibration frequencies in the ground and first excited electronic states is about 20 cm(-1) without modification of initial parameters, used in the MO/8 model.